Recently, interest in soy isoflavones has increased around the world because epidemiologic studies have shown that the consumption of soy isoflavones may be associated with both low incidence rates of certain cancers, such as breast cancer, prostate cancer, uterine cancer, colon cancer, etc., and reduction in the risk of various diseases including cardiovascular problems, osteoporosis and menopausal symptoms. In 1996, Food and Drug Administration of the USA approved selling soy isoflavones as health food or supplement on the market. At present, the soy isoflavone products are popular in Europe and the USA.
Isoflavones are a flavanoid subgroup found in a variety of plants, with significantly high amounts in soybeans. Natural soybeans contain 1.2-4.2 mg of total isoflavones /g of sample, with large variation due to variety, crop year and growth location, whereas the content in soybean products (i.e. tofu, miso, soy protein, soy milk) generally does not exceed 0.2% dry weight. To date, twelve main isoflavones (Table 1, Rostagno et al., 2004, Analytica Chimica Acta, 522: 169-177) have been characterized in soybeans and soybean products including genistein, daidzein and glycitein and their respective malonyl, acetyl and glucosyl forms. The three families of genistein, daidzein and glycitein are found in an approximate ratio of 6:3:1. It should be noted that most of isoflavones are present in the form of glucosides in natural soybeans and non-fermented soy products (soy protein, soy milk, etc.), with genistin and daidzin accounting for the major portion, and only 2 to 5% of isoflavones are aglycones, but the physiological effects of soy products are mainly contributed by their aglycones.
TABLE 1Aglycones: CompoundsSymbolR1R2DaidzeinDeHHGlyciteinGleHOCH3GenisteinGeOHHGlucosides: CompoundsR1R2R3DaidzinDiHHHGlycitinGlyHOCH3HGenistinGiOHHHAcetyldaidzinAcDiHHCOCH3AcetylglycitinAcGlyHOCH3COCH3AcetylgenistinAcGiOHHCOCH3MalonyldaidzinMDiHHCOCH2COOHMalonylglycitinMGlyHOCH3COCH2COOHMalonylgenistinMGiOHHCOCH2COOH
Soy isoflavones have been reported to have a variety of biological activities. Due to the estrogenic activity of isoflavones, nowadays they are used instead of traditional hormone replacement therapy (HRT) for treating estrogen-deficient women in menopause or postmenopause.
One better alternative is soy isoflavones. Since isoflavones structurally resemble genuine 17β-estradiol (E2) and have weak estrogenic activities, they can mimic or modulate the actions of endogenous estrogens in vertebrates by binding to estrogen receptors (ERs). For example, genistein shares structural features with the potent estrogen E2, so it can exert estrogenic activity.
Structure of an isoflavone (genistein) is relative to that of endogenous estrogen (17β-estradiol).
Many problems have been found in the processes for manufacturing soy isoflavones. Firstly, repeated extraction with organic solvents or separation by chromatography was used to purify soy isoflavones in most prior art techniques. But these two methods are not only costly but also too complicated to be applied for a large-scale production. Secondly, toxic organic solvents including acetone, ether, hexane, chloroform, etc. were extensively used. But the remains of these toxic solvents in the products will likely endanger human health when these products are used for making drugs, foods, cosmetics, etc.